1. Field of the Invention
The present invention is related to a high-dielectric sheet, a printed circuit board having the high-dielectric sheet, and methods of producing the high-dielectric sheet and printed circuit board.
2. Discussion of the Background
A high-dielectric sheet is used as a thin-film capacitor provided inside a printed circuit board (herein after referred to as “PCB”). Japanese Unexamined Patent Publication 2005-191559 describes a method of producing a high-dielectric sheet. In this method, a 1.2 μm-thick high-dielectric layer is formed on a copper foil by repeating several times a process in which a mixed solution of diethoxy barium and titanium bitetraisopropoxide is hydrolyzed to make a sol-gel solution, which is spincoated, dried and calcined on the copper foil. Then, a copper foil is formed on the high-dielectric layer by vacuum deposition. The above reference also discusses a method for forming a high-dielectric layer by sputtering using barium titanate as a target material.
However, in this method, when a high-dielectric layer is formed by using a sol-gel solution, pinholes may occur after organic materials or solvents are decomposed or evaporate during the process of forming the high-dielectric layer. Such pinholes are unwelcome, since they may become the starting points of cracks. Also, plating liquids may seep into those pinholes when plating a metal foil on the high-dielectric layer, thereby forming a conductor running through the high-dielectric layer and potentially causing short-circuits. Furthermore, when a high-dielectric layer is formed by sputtering, pits (hollows) may occur on the surface. Such pits are not welcome, since they may also become the starting points of cracks in the high-dielectric layer. It is thus desired to produce a high-dielectric layer by a method which does not produce cracks in the high-dielectric layer and short-circuits between electrodes. The contents of the above publication are herein incorporated by reference in their entirety.